pH sensitivity of chlorophyll fluorescence quenching is determined by the detergent/protein ratio and the state of LHCII aggregation

AbstractHere we show how the protein environment in terms of detergent concentration/protein aggregation state, affects the sensitivity to pH of isolated, native LHCII, in terms of chlorophyll fluorescence quenching. Three detergent concentrations (200, 20 and 6μM n-dodecyl β-d-maltoside) have been tested. It was found that at the detergent concentration of 6μM, low pH quenching of LHCII is close to the physiological response to lumen acidification possessing pK of 5.5. The analysis has been conducted both using arbitrary PAM fluorimetry measurements and chlorophyll fluorescence lifetime component analysis. The second led to the conclusion that the 3.5ns component lifetime corresponds to an unnatural state of LHCII, induced by the detergent used for solubilising the protein, whilst the 2ns component is rather the most representative lifetime component of the conformational state of LHCII in the natural thylakoid membrane environment when the non-photochemical quenching (NPQ) was absent. The 2ns component is related to a pre-aggregated LHCII that makes it more sensitive to pH than the trimeric LHCII with the dominating 3.5ns lifetime component. The pre-aggregated LHCII displayed both a faster response to protons and a shift in the pK for quenching to higher values, from 4.2 to 4.9. We concluded that environmental factors like lipids, zeaxanthin and PsbS protein that modulate NPQ in vivo could control the state of LHCII aggregation in the dark that makes it more or less sensitive to the lumen acidification. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy

The influence of light and tidal exposure on primary production in the tropical seagrass Zostera capricorni and Halophila ovalis

The growth, survival and depth penetration of seagrass is directly related to light availability, which drives photosynthesis. The amount of light reaching seagrass beds is highly variable and can be easily disrupted by human activities, such as dredging. Dredging results in increased turbidity and decreased light penetration to the seagrass beds, invariably influencing overall productivity and seagrass health. To better understand seagrass light requirements and resilience to environmental stressors such as dredging requires knowledge on seagrass photophysiology and the impact air exposure during a tidal cycle has on photosynthesis. Oxygen, fluorescence and bio-optical properties were measured over a tidal cycle in seagrass beds of Zostera capricorni and Halophila ovalis in Gladstone Harbour to provide insight into the variability in carbon production in intertidal seagrass meadows. Both species showed an increase in photosynthetic activity with increased irradiance as the tide receded. However, sensitivity to desiccation was observed during air-exposure with a significant decline in photosynthesis irrespective of increased light availability. Understanding the complex dynamics of seagrass photosynthesis over a tidal cycle will help in the mitigation of dredging-related light loss to Gladstone seagrass meadows

The microbiological drivers of temporally dynamic Dimethylsulfoniopropionate cycling processes in Australian coastal shelf waters

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in O’Brien, J., McParland, E. L., Bramucci, A. R., Ostrowski, M., Siboni, N., Ingleton, T., Brown, M. V., Levine, N. M., Laverock, B., Petrou, K., & Seymour, J. The microbiological drivers of temporally dynamic Dimethylsulfoniopropionate cycling processes in Australian coastal shelf waters. Frontiers in Microbiology, 13, (2022): 894026, https://doi.org/10.3389/fmicb.2022.894026.The organic sulfur compounds dimethylsulfoniopropionate (DMSP) and dimethyl sulfoxide (DMSO) play major roles in the marine microbial food web and have substantial climatic importance as sources and sinks of dimethyl sulfide (DMS). Seasonal shifts in the abundance and diversity of the phytoplankton and bacteria that cycle DMSP are likely to impact marine DMS (O) (P) concentrations, but the dynamic nature of these microbial interactions is still poorly resolved. Here, we examined the relationships between microbial community dynamics with DMS (O) (P) concentrations during a 2-year oceanographic time series conducted on the east Australian coast. Heterogenous temporal patterns were apparent in chlorophyll a (chl a) and DMSP concentrations, but the relationship between these parameters varied over time, suggesting the phytoplankton and bacterial community composition were affecting the net DMSP concentrations through differential DMSP production and degradation. Significant increases in DMSP were regularly measured in spring blooms dominated by predicted high DMSP-producing lineages of phytoplankton (Heterocapsa, Prorocentrum, Alexandrium, and Micromonas), while spring blooms that were dominated by predicted low DMSP-producing phytoplankton (Thalassiosira) demonstrated negligible increases in DMSP concentrations. During elevated DMSP concentrations, a significant increase in the relative abundance of the key copiotrophic bacterial lineage Rhodobacterales was accompanied by a three-fold increase in the gene, encoding the first step of DMSP demethylation (dmdA). Significant temporal shifts in DMS concentrations were measured and were significantly correlated with both fractions (0.2–2 μm and >2 μm) of microbial DMSP lyase activity. Seasonal increases of the bacterial DMSP biosynthesis gene (dsyB) and the bacterial DMS oxidation gene (tmm) occurred during the spring-summer and coincided with peaks in DMSP and DMSO concentration, respectively. These findings, along with significant positive relationships between dsyB gene abundance and DMSP, and tmm gene abundance with DMSO, reinforce the significant role planktonic bacteria play in producing DMSP and DMSO in ocean surface waters. Our results highlight the highly dynamic nature and myriad of microbial interactions that govern sulfur cycling in coastal shelf waters and further underpin the importance of microbial ecology in mediating important marine biogeochemical processes.This research was supported by the Australian Research Council Grants FT130100218 and DP180100838 awarded to JS and DP140101045 awarded to JS and KP, as well as an Australian Government Research Training Program Scholarship awarded to JO’B

Hot spots and hot moments in seagrass 'blue carbon' science

When seagrass meadows are destroyed, what happens to the 'blue carbon' stored within their sediments; does it stay in the ground, or is it released into the atmosphere? Is it possible to manage seagrass ecosystems so that they sequester more blue carbon? With seagrasses now recognised as globally-significant carbon sinks, the answers to these questions have important consequences for nature-based climate change mitigation and adaptation (i.e. 'biosequestration'). We make the case that microbes fundamentally control the fate of sequestered blue carbon within seagrass, and, therefore, management efforts aimed at bolstering blue carbon opportunities within seagrass ecosystems need to target processes that influence (directly or indirectly) microbial remineralisation of blue carbon. New data will be presented showing that blue carbon occurs in hotspots and changes in the geochemistry of seagrass sediments - such as those caused by disturbance - can create hot moments, whereby organic carbon within sediments undergoes rapid and substantial microbial remineralisation. In order to better manage seagrass ecosystems for blue carbon benefits, we outline three recommendations: reducing anthropogenic nutrient inputs, reinstating top-down control of bioturbator populations, and restoring hydrology. These processes are amenable to management control, they promote microbial dormancy and limit microbial priming, and offer ecosystem benefits beyond carbon sequestration

Biogeographical and seasonal dynamics of the marine Roseobacter community and ecological links to DMSP-producing phytoplankton

Abstract Ecological interactions between marine bacteria and phytoplankton play a pivotal role in governing the ocean’s major biogeochemical cycles. Among these, members of the marine Roseobacter Group (MRG) can establish mutualistic relationships with phytoplankton that are, in part, maintained by exchanges of the organosulfur compound, dimethylsulfoniopropionate (DMSP). Yet most of what is known about these interactions has been derived from culture-based laboratory studies. To investigate temporal and spatial co-occurrence patterns between members of the MRG and DMSP-producing phytoplankton we analysed 16S and 18S rRNA gene amplicon sequence variants (ASVs) derived from 5 years of monthly samples from seven environmentally distinct Australian oceanographic time-series. The MRG and DMSP-producer communities often displayed contemporaneous seasonality, which was greater in subtropical and temperate environments compared to tropical environments. The relative abundance of both groups varied latitudinally, displaying a poleward increase, peaking (MRG at 33% of total bacteria, DMSP producers at 42% of eukaryotic phototrophs) during recurrent spring-summer phytoplankton blooms in the most temperate site (Maria Island, Tasmania). Network analysis identified 20,140 significant positive correlations between MRG ASVs and DMSP producers and revealed that MRGs exhibit significantly stronger correlations to high DMSP producers relative to other DMSP-degrading bacteria (Pelagibacter, SAR86 and Actinobacteria). By utilising the power of a continental network of oceanographic time-series, this study provides in situ confirmation of interactions found in laboratory studies and demonstrates that the ecological dynamics of an important group of marine bacteria are shaped by the production of an abundant and biogeochemically significant organosulfur compound

Development of a Light-Based Seagrass Management Approach for the Gladstone Western Basin Dredging Program

This report presents a light-based management approach to protect Gladstone seagrasses from dredge plume impacts associated with the Western Basin dredging program. The management plan and trigger levels are based on findings from two years of seagrass research in Gladstone directed at establishing the required light levels for local seagrass survival. The light trigger values and timelines for managing seagrass impacts are based on a multi-faceted approach including the ongoing Seagrass Health Study programs and a review of historical seagrass trends from permanent transect monitoring sites and associated benthic PAR recordings. This combined work has led to a working light trigger value of 6 mol m-2 d-1 over a rolling two week average, under which management actions and alerts are proposed to ensure appropriate steps are taken to mitigate seagrass declines

Single-Cell Biomolecular Analysis of Coral Algal Symbionts Reveals Opposing Metabolic Responses to Heat Stress and Expulsion

The success of corals in nutrient poor environments is largely attributed to the symbiosis between the cnidarian host and its intracellular alga. Warm water anomalies have been shown to destabilize this symbiosis, yet detailed analysis of the effect of temperature and expulsion on cell-specific carbon and nutrient allocation in the symbiont is limited. Here, we exposed colonies of the hard coral Acropora millepora to heat stress and using synchrotron-based infrared microspectroscopy measured the biomolecular profiles of individual in hospite and expelled symbiont cells at an acute state of bleaching. Our results showed symbiont metabolic profiles to be remarkably distinct with heat stress and expulsion, where the two effectors elicited opposing metabolic adjustments independent of treatment or cell type. Elevated temperature resulted in biomolecular changes reflecting cellular stress, with relative increases in free amino acids and phosphorylation of molecules and a concomitant decline in protein content, suggesting protein modification and degradation. This contrasted with the metabolic profiles of expelled symbionts, which showed relative decreases in free amino acids and phosphorylated molecules, but increases in proteins and lipids, suggesting expulsion lessens the overall effect of heat stress on the metabolic signature of the algal symbionts. Interestingly, the combined effects of expulsion and thermal stress were additive, reducing the overall shifts in all biomolecules, with the notable exception of the significant accumulation of lipids and saturated fatty acids. This first use of a single-cell metabolomics approach on the coral symbiosis provides novel insight into coral bleaching and emphasizes the importance of a single-cell approach to demark the cell-to-cell variability in the physiology of coral cellular populations

Parvilucifera sinerae, un parasito generalista

XII Reunión Ibérica sobre Microalgas Nocivas y Biotoxinas, 17-18 de octubre de 2013, Palma de MallorcaLos parasitoides son una de las causas de mortalidad de las microalgas, pero los mecanismos y estrategias que éstos han desarrollado para infectar las algas son desconocidos. Aquí mostramos que el parasitoide generalista de dinoflagelados Parvilucifera sinerae (Perkinsozoa, Alveolata) se activa desde su estado durmiente tanto por células de Alexandrium minutum como por exudados del cultivo del huesped. Identificamos el metabolito algal dimetilsulfuro (DMS) como la molécula señal denso-dependiente que indica la presencia de huéspedes potenciales. Esto permite al parasitoide alternar entre un estadio de esporangio durmiente y uno libre e infectivo químicamente activado. Exudados ricos en DMS de dinoflagelados resistentes también inducen la activación del parasitoide. Estos resultados amplían la importancia de los compuestos dimetilados de azufre en la ecología química marina, los cuales han sido descritos como moléculas señal y quimioatrayentes para mamíferos, pájaros, peces, invertebrados y microbios planctónicosPeer Reviewe

A Game of Russian Roulette for a generalist dinoflagellate parasitoid: host susceptibility is the key to success

17th International Conference on Harmful Algae (ICHA), 9-14 October 2016, Florianópolis, Santa Catarina, Brazil.-- 1 pageMarine microbial interactions involving eukaryotes and their parasites play an important role in shaping phytoplankton communities. These interactions may alter densities of the main host, which in turn have consequences for the concurrent species. The effect that generalist parasitoids exert on a community is strongly dependent on the degree of host specificity. Parvilucifera sinerae is a generalist parasitoid able to infect a wide range of dinoflagellates, including toxic-bloom-forming species. A density-dependent chemical cue is the trigger for the activation of the infective stage, but the seek strategy of its host is completely different. In the infective stage, P. sinerae is able to sense potential hosts, but does not actively select among them. Instead, the parasitoids contact the host at random and once encountered, the chance to penetrate inside and develop the infection strongly depends on the degree of host susceptibility. As such, their strategy for persistence is more of a game of Russian roulette, where the chance of survival is dependent on the host susceptibility. Our study identifies P. sinerae as a potential key player in community ecology, where in mixed dinoflagellate communities consisting of hosts that are highly susceptible to infection, parasitoid preferences may mediate coexistence between host species, reducing the dominance of the superior competitor. Alternatively, it may increase competition, leading to species exclusion. If, however, highly susceptible hosts are absent, the parasitoid population could suffer a dilution effect maintaining a lower parasitoid density. Therefore, both host community structure and host susceptibility will determine infectivity in the fieldPeer Reviewe